Global warming discussions are done no service by their usual origins in anecdote. A pair of neighbors may talk over the hedgerow after a week of summer swelter and decide this is evidence of the phenomenon. The opposite is of ten true as well. A particularly icy winter month leads to a throwing up of the hands, "So much for global warming," they'll say.

Both are shortsighted, and on global warming, shortsightedness is the cardinal sin. There is no substitute for long-term data - the collection of millions of anecdotes (i.e. data points) over thousands of years. And on this issue, we have just that. The Earth, inarguably, is warming. Most scientists believe human activity has played a role. A vocal minority believes the current warming is part of a natural cycle.

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